Method of manufacturing a conductive coated sheet and said sheet



June 8, 1954 RUBIN 2,680,699

METHOD OF MANUFACTURING A CONDUCTIVE COATED SHEET AND SAID SHEET FiledApril 21, 1952 COPPER PLATE PAPER EVAPORATED FILM THERMOSLTTING PLASTICRESIN APPLIED As LIQUID AND INITIALLY THERMOSETT'NG PLATE PARTLY CURED0R SHEET INVENTOR. M1/70r7 iP Patented June 8, 1954 METHOD OFMANUFACTURING A CGNDUC- TIVE COATED SHEET AND SAID SHEET Milton D.Rubin, Dorchester, Mass.

Application April 21, 1952, Serial No. 283,287

12 Claims. 1

The present invention relates to a method of producing a laminated sheethaving a top surface formed as highly conductive film coating or platingbeneath which are non-conducting layers of other material and to theproduct itself. Such articles are useful in so called printed circuitswherein electrical circuits are formed from such sheet material byetching, cutting or removing in some other fashion certain portions ofthe conductive film or coating leaving other portions of the conductingfilm or coating forming the circuit to which electrical elements areconnected at various points.

One of the great difficulties in producing circuits of this nature isthat the plating is not usually sufficiently permanent and will after aperiod of wear separate from its supporting plate or sheet causingeither a break in the circuit or creating sections of very highresistance which makes the circuit useless. also been experienced inproviding coated or plated sheets of the present type. In many cases thecoating is not uniform and often has voids where little or no metal hasbeen deposited causing irregular electrical characteristics and therebygreatly affecting the design of the apparatus in which the sheets areused. It is extremely essential in all cases to provide a durable,strong sheet or plate on which the copper or other conductive layer isfirmly attached with uniform thickness and constant homogeneity suchthat the conductivity is uniform throughout the whole sheet.

Various methods have previously been tried such as cementing a foil to aplastic base and spraying a coating on a plastic or other base, butneither of these methods have provided sulficiently strong and durablesheets with homogeneous conductive surfaces to warrant their continuoussuccessful use.

By the present invention it is possible to secure to a non-conductivesheet or plate, a thin conductive coating or layer which willpermanently ad here to the sheet and will not, even with rough usage,part from the sheet, be flaked oli from the sheet or be removed by anyordinary usage or wear of the sheet. When a circuit is to be formed onthe sheet, the parts desired to be removed may be removed by etching,cutting or other suit able means, but they will otherwise adhere durablyand permanently.

Without further describing the merits and ad vantages of the presentinvention which will be more clearly understood from the specificationset forth below, the invention will now be de- Other difficulties havescribed in connection with a drawing illustrating an embodiment of thestructure of the plate or sheet of the present invention which shows asection therethrough. In the process herein employed, a porous thinsheet material, such as a paper or paper-like material or a sheet whichmay be of woven or knitted fabric, such as cotton, linen or syntheticmaterials or which may be made of paper and synthetic materials, is usedas the initial sheet base. Such a sheet should be thin as a paper sheetand should be flexible and readily impregnable with the liquids whichwill later be mentioned.

I have found that for the most part a fairly good grade of kraft paperis very satisfactory since such paper is sufficiently porous to acceptthe impregnating liquids used in the present invention.

The kraft paper shown at l in the diagram is coated with a very thinfilm 2 of evaporated conductive metal. Silver is preferable for thispurpose and the coating or film may be deposited in any of the wellknown manners. Evaporation process is preferable since by this method auniform very thin coating or layer of the metal may be obtained. Besidessilver, other suitable metals, for instance, as aluminum, copper, mayalso be used.

After the thin silver film or coating which has a thickness in the rangeof a micron or thereabouts, that is a thickness substantially less than0.001 there is plated on to the film a copper plate which may be done ina continuous process by dipping or by any other suitable means, as forinstance, as electrolytic process. This copper plate may be .001" ormore, and while copper is preferable, again it is possible to useanother conductive element such as silver if that is desired. The sheetwhich then comprises a krait paper thin sheet with a continuous platedcopper film is then thoroughly washed and allowed to dry.

The copper plate should so coat one side of the sheet that no openingsremain on the sheet where no copper has been deposited so that acontinuous uniform plated copper sheet is obtained. After the sheet hasbeen dried the non-plated side is brushed with a thermosetting plasticcoating or the coating may be applied in any other suitable way. Such acoating is thoroughly absorbed by the kraft sheet so that it becomesimpregnated right through to the back of the copper plate. I'he excessmay be wiped off. I preferably use for this purpose aphenol-formaldehyde varnish compatible with the other materials used andwhich is thermosetting in character and will withstand curingtemperatures employed or some other thermosetting plastic viscous resinsuch as a urea-formaldehyde, silicone, vinyl, etc. This impregnation isthen partially cured, which may be accomplished by heating the sheet atapproximately 250 F. for a few minutes. Care must be taken to cure thesheet only partially since a further cure is necessary to complete theproduct. This sheet is then laid upon a partially or fully cured basesheet such as a phenolic resin base sheet or a linen base sheetimpregnated with the phenol material or any of the usual thermosettingresins, plastic sheets or plates which may be ti emselves laminates ofwoven fabrics, reinforced fiber, fill d or other types of sheets. Thecopper plate sheet with its partially cured resin base is then madeintegral with the thermo-setting'base sheet by heat and pressure whichusually is accomplished. by pressures up to 250 lbs. to 300lbs.

per square inch at temperatures of 350 F. to 400 for a short period ofapproximately minutes or more. Lower temperatures and pressures thanthose given may be used. With a partially cured base sheet more timemust be allowed for curing the entire plate dependent upon the thicknessof the base.

I find that certain features in this process must be carefully observed.

(1) None of the varnish or thermosetting viscous liquid applied to theback of the kraft paper must be permitted to force its way through themetal coating so as to appear on the face of the metal coating. This ishighly detrimental to the sheet itself.

(2) The paper or other material immediately I in back of the film andconductive plate must either be somewhat porous or have microscopicrecesses of sufiicient area so that the impregnant put in the back ofthe paper will penetrate through the interstices and reach the depositedfilms and plating.

(3) Care must be taken that a continuous film is deposited on the kraftpaper and that similarly the plate is deposited uniformly over the film.

(4) In the final curing of the composite sheet the sheet must be putunder suitable pressure and while such pressure is not readily definablebecause it depends to some extent upon the kind of paper or initialsheet on which the film is deposited as well as upon the other elementswhich are used, the pressure must be such as to fill substantially allthe depressions or interstices in the paper or fabric sheet which isused. While it is preferable to use pressures in the range of 200 lbs.to 300 lbs. per square inch in effecting the final bond, other pressuresmay be used. Higher pressures may be used for thicker and less porouslayers.

(5) It is highly essential in the present methed to deposit the film andplate the metal on the paper sheet before applying to the reverse sideof the sheet the thermosetting varnish or other materials used inbonding the sheet on its ultimate back plate.

It has been mentioned above that the initial film. is deposited on thekraft or other sheet by evaporation. In the sense as used in the presentapplication, evaporation includes any means by which the metal isvaporized and allowed to settle upon the sheet. Such for instance asheating the metal under vacuum conditions to provide a vaporor-obtaining the same general eifectby electric sputtering or otherequivalent means.

Having now described my invention, I claim:

1. A method of manufacturing a plate or sheet having an electricalconductive non-alkali metallic plated coating which comprises taking abase sheet of flexible, impregnable paper material, evaporating anon-alkali metallic film on one surface thereof, then plating over thefilm a continuous non-alkali metallic coating, washing, rinsing anddrying the sheet, impregnating the unplate'd side only with a liquidthermosetting resin, partially curing the same on the sheet and finallycuring to the partially cured face of said sheet with heat and pressurea thermosetting basesheet.

2. A method of'manufacturing a plate or sheet having an electricalconductive non-alkali metallic plated coating which comprises taking abase sheet of flexible, impregnable paper material, evaporating anon-alkali metallic film on one surface thereof, then plating over thefilm a continuous copper plate, washing, rinsing and dryingthe sheetimpregnating the unplated side only with a liquid thermosetting resin,partially curing the same on the sheet and finally curing to thepartiallycured face of the sheet with heat and pressure, a thermosettingbase sheet.

3. A method of manufacturing a plate or sheet having an electricalconductive non-a1kali metallic plated coating which comprises taking a.base sheet of kraft paper, evaporating a conductive non-alkali metallicfilm of athickness of substantially less than 0.001" on one side of saidsheet, then plating over said film a continuous non-alkali metalliccoating having a thickness of substantially 0.001" and greater, washing.rinsing and drying the sheet, impregnating the unplated side only with athermosetting resin, partially curing the same'on the sheet and finallycuring to the partially cured face of the sheet a thermosettingbasesheet with heat and pressure.

'4, A method'of manufacturing a plate or sheet having anelectricalconductive non-alkali metallic plated coating which comprises taking abase sheet of kraft paper, evaporating a conductive non-alkali metallicfilm of a thickness of substan tially less than 0.001" on 'one'side ofsaid sheet, then plating over said film with a continuous non-alkalimetallic coating having a thickness of substantially 0.001" and greater,washing,

rinsing and drying the sheet impregnating the unplated side only with athermosetting resin, partially and finally curing the same on the sheetand finally securing to the said sheet on the un plated face a heavierbase sheet.

5. A plate or sheet having a conductive nonalkali metallic platedcoating comprising a sheet of paper material having deposited on oneside thereof a thin non-alkali metallic film of several microns thick aconductive non-alkali metallic plated coating deposited. on saidnon-alkali metallic film of substantially .001" in thickness, athermosetting plastic resin forming a coating over, filling theinterstices in said paper sheet and impregnating said paper from theside opposite to that on which aid metallic film is formed and athermosetting sheet cured to said thermosetting plastic resinouscoating.

6. A plate or sheet having a conductive nonalkalimetallic plated coatingcomprising a sheet of paper material having evaporated on one sidethereof thereon a thin silver film of substantially a micron thick, anelectrolytic plating deposited on said silver film forming'a continuousconductive'non-alkali metallic surface of substantially uniformthickness, a thermosetting plastic resinous coating impregnating onlythe unplated face the paper sheet but free of the paper sheet but freefrom the continuous metallic surface and partially cured to said papersheet, and a thermosetting resinous plate secured to said partiallycured surface.

'7. A plate or sheet having a conductive nonalkali metallic platedcoating comprising a sheet of paper material having evaporated on oneside thereof a thin silver film of substantially a micron thick, anelectrolytic plating deposited on said silver film forming a continuousconductive non-alkali metallic surface of substantially uni formthickness, a thermosetting plastic resinous coating impregnating onlythe unplated face of from the continuous metallic surface and partiallycured to said paper sheet and a phenolic resinous sheet secured thereto.

8. A method of manu acturing a plate or sheet having an electricalconductive non-alkali metallic plated coating which comprises taking abase sheet of flexible, impregnable paper material, evaporating anon-alkali conductive metallic film on only one surface thereof, thenplating over the film with a continuous conductive non-alkali metalliccoating, washing, rinsing and drying the sheet, impregnating theunplated side only with a liquid th rmosetting resin, partially curingthe same on the sheet and finally curing to the partially cured face ofsaid sheet with heat and pressure a partially cured thermosetting basesheet.

9. A method of manufacturing a plate or sheet having an electricalconductive non-alkali metallic plated coating which comprises taking abase sheet of flexible, impregnable paper material, evaporating anon-alkali conductive metallic film on only one surface thereof, thenplating over the film with a continuous conductive non-alkali metalliccoating, washing, rinsing and drying the sheet, impregnating theunplated side only with a liquid thermosetting resin, partially curingthe same on the sheet and finally curing to the partially cured face ofsaid sheet with heat and pressure a fully cured therinosetting basesheet.

10. A plate or sheet having a conductive nonalltali metallic platedcoating comprising a sheet of paper material having deposited on oneside thereof a thin metallic non-alkali film of substantially less than.001, a conductive non alkali metallic coating plated on said film ofthe order of .001 in thickness providing a continuous closed surface anda thermosetting plastic resin forming a coating on the other side of thesheet and impregnating said paper but leaving the plated side of thesheet forming a continuous metallic surface.

11. A plate or sheet having a conductive nonalkali metallic platedcoating comprising a sheet of paper material having deposited on oneside thereof a thin metallic non-alkali film of substantially onemicron, a conductive non-alkali metallic coating plated on said film ofthe order of .001" in thickness providing a continuous closed surfaceand a thermosetting plastic resin forming a coating on the other side ofthe sheet and impregnating said paper but leaving the plated side f thesheet forming a continuous metallic surface.

12. A plate or sheet having a conductive nonalkali metallic platedcoating comprising a sheet or paper-like material having deposited onone side thereof a thin metallic non-alkali film of substantially lessthan .001", a conductive nonallcali metallic coating plated on said filmof substantially .001" in thickness and a thermosetting plastic resinforming a coating on the other side of the sheet and impregnating saidpaper but leaving the plated side of the sheet forming a continuousmetallic surface, said coating and impregnation being cured in the sheetso formed.

References Cited in the file of this patent UNITED STATES PATENTS Number

1. A METHOD OF MANUFACTURING A PLATE OR SHEET HAVING AN ELECTRICAL CONDUCTIVE NON-ALKALI METALLIC PLATED COATING WHICH COMPRISES TAKING A BASE SHEET OF FLEXIBLE, IMPREGNABLE PAPER MATERIAL, EVAPORATING A NON-ALKALI METALLIC FILM ON ONE SURFACE THEREOF, THEN PLATING OVER THE FILM A CONTINUOUS NON-ALKALI METALLIC COATING, WASHING, RINSING AND DRYING THE SHEET, IMPREGNATING THE UNPLATED SIDE ONLY WITH A LIQUID THERMOSETTING RESIN, PARTIALLY CURING THE SAME ON THE SHEET AND FINALLY CURING TO THE PARTIALLY CURED FACE OF SAID SHEET WITH HEAT AND PRESSURE A THERMOSETTING BASE SHEET.
 5. A PLATE OR SHEET HAVING A CONDUCTIVE NONALKALI METALLIC PLATED COATING COMPRISING A SHEET OF PAPER MATERIAL HAVING DEPOSITED ON ONE SIDE THEREOF A THIN NON-ALKALI METALLIC FILM OF SEVERAL MICRONS THICK, A CONDUCTIVE NON-ALKALI METALLIC PLATED COATING DEPOSITED ON SAID NON-ALKALI METALLIC FILM OF SUBSTANTIALLY .001'''' IN THICKNESS, A THERMOSETTING PLASTIC RESIN FORMING A COATING OVER FILLING THE INTERSTICES IN SAID PAPER SHEET AND IMPREGNATING SAID PAPER FROM THE SIDE OPPOSITE TO THAT ON WHICH SAID METALLIC FILM IS FORMED AND A THERMOSETTING SHEET CURED TO SAID THERMOSETTING PLASTIC RESINOUS COATING. 